How the Repayment Calculator works
This is the general-purpose repayment view: give it the balance, rate and term and it returns the level payment that clears the debt exactly at the end of the term.
Payment = P × r ÷ (1 − (1 + r)^−n), where P is the amount borrowed, r is the monthly rate (APR ÷ 12) and n is the number of monthly payments.